Kills me that no one with the opportunity to ask has ever asked which of those was meant to be the origin of Ulti's name. Kind of seems like both the "ultimate" and "Artemisia" influences may have been incorporated -- perhaps after starting at one and realizing the applicability of the transliteration of the other?
At the very least, I do think "ultimate" is part of the intention there, in part because FFVIII was the first game to get an Ultimania, and the introduction to that book explains that the name "Ultimania" was derived from mashing "ultimate" and "mania" together. That sense of "ultimate" as something wholly comprehensive/all in one obviously fits Ultimecia.